1. Field of the Invention
The invention relates to the treatment of sewage and in particular, though not exclusively, to sewage treatment for use on a mobile platform such as a ship.
2. Discussion of Prior Art
Disposal of sewage from ships alongside or in coastal waters is a considerable current problem. Some harbours have sewage collection facilities, however, these are not always available. Thus sewage collection and treatment plant is required where port facilities are unavailable. Such plant is desirably highly efficient such that a small plant will allow a ship to remain alongside for a long period. Currently there are three types of sewage treatment plant in common use. These are:
(a) Collect, hold and transfer (CHT) with either gravity or vacuum collection systems. PA0 (b) Solid separation treatment plant (SSTPS). PA0 (c) Biological sewage treatment plants (BSTPS). PA0 (1) Changes in the salinity of the flush water. PA0 (2) High hydraulic loads caused by defective toilet flushing valves or leaking tank cleaning spray cross connection valves. PA0 (3) Variations in the load cycle imposed by the operating pattern of the ship. Low loads are particularly detrimental as the bacterial population necessary for aerobic digestion of the sewage cannot be sustained. PA0 (4) Excessive use of detergents and cleaning agents which destroy the bacterial population. PA0 (a) The level of biological activity of the discharge does not meet the standard expected to be set by international regulations. PA0 (b) The filters have proved to be particularly troublesome. They block frequently and require considerable and unpleasant maintenance. PA0 (c) The plants have a relatively short holding time of only 5-7 days. PA0 (d) The plants use a lot of disinfectant (151 lbs/day).